It is
difficult to design refrigeration for mobile applications like
boats and RVs. What works in an RV may not work in a boat. RV’s
have front door openings and exterior air vents for condenser
and compressor heat disposal while boats usually have top
loading hatches and no interior vents. Also freezing-chamber
evaporators can not always be located above refrigerator areas.
There are a number of ways to improve and expand a mobile
refrigerator’s efficiency by adding circulating or heat disposal
fans such as the following installation applications:

Normal heat
removal from a refrigerator’s condenser, or electronics and even
the compressor itself may not be as efficient as it should be.
So how can a fan be added to move this unwanted heat away?To control the exhaust fan or add a
condenser fan I have used a snap action fan control thermostat
switches available from www Granger at a cost of $12. A fan
should only be operated as needed. Their p/n is 2E245 they close
at 110˚F and open contacts below 90˚F. When attached to a line
from the compressor or warmest spot on refrigerator’s condenser
with plastic tie wraps the fan will run when the compressor
heats the outlet tubing or condenser coil above 110˚F and shuts
off the fan when temperature switch drops to 90˚. Power wire for
this fan circuit must be fused to the correct size. This snap
action switch is good for 10 amps at 12 or 110 volts. See
Granger catalog.

For a spillover box to have two efficient temperature areas
there needs to be at least a 25˚F temperature difference (Delta
T) from one side of the divider to the other. A spillover
divider should have at least an insulating R value of 10.

A
small fan located midway up on the divider along with an equal
size return hole at top of divider will provide circulation
between sections. The main thermostat controls the freezer
average temperature by monitoring the evaporator temperature.
The divider fan controlling refrigerator temperature will be
controlled by a separate thermostat with its temperature probe
located in refrigerator section.

For reasons of energy efficiency small refrigeration units use a
thermostat that is calibrated for evaporator temperature instead
of box temperature. When selecting a thermostat for controlling
a divider fan, it must have its range control from 20 to 40˚F.
In some cases these zone control thermostats are identified as
Cooler box thermostats or the more expensive units are called
Temperature controllers and they range from -20 to +40˚ F.

Divider fans must be small for two reasons
since too much air movement when the fan is running will raise
freezer temperature and when the fan is not running, a large fan
opening may change the Delta T between box areas. I have used a
number of the one inch square ½ inch thick 12 volt Radio Shack
Fans. Tey seem to last on live aboard boats 4 to 5 years even at
low temperatures. Years ago I used the 3 1/8 inch muffin fans
that move 25 CFM but they were too large. This is the
information on divider fan I recommend now selling for $12.

The wiring for this divider
fan would require a 1 amp fuse, an Off-On
switch, and zone temperature thermostat. Since
the fan is operated by transistors correct wire
polarity is important. Because this divider fan
is a separate system from the refrigeration
unit, it must operate when the refrigeration
unit is cycled off so it will not be connected
to the BD compressor’s fan circuit. Twin red and
black wires of 20 gauge or larger is OK for a
fan as long as a one amp fuse is installed at
the power source. Fan power must be available
anytime the refrigerator box is intended to be
kept cold.

Very few
boat icebox conversion Spillover refrigerators function properly
because basic thermodynamic, simple principals are ignored. A
separating divider between a refrigerator and a high temperature
freezer of +15 to +22˚F needs an insulating value of at least
R5. Two inches of extruded polystyrene with impact resistant
material on each side will provide a temperature difference
between separated areas of 20˚F. To extend the flavor quality of
food stored for more than three weeks the freezer temperature
range should be zero to +15˚F. Then the divider will need to be
insulated to R10 to R15. In assembling a spillover system or any
refrigerator or freezer think about incorporating these
principals so they work for you instead of against you.

In a
static state, air is a bad conductor of heat. When air is
trapped and can’t move, it becomes a good insulator. Heat
conduction occurs when two objects
at different temperatures are in contact with each other. Heat
flows from the warmer to the cooler object until they are both
at the same temperature. For air to be a good conductor of heat,
there must be movement and collision of its molecules, therefore
there must be air movement inside the box at all times.

The warmer the air is the less dense it is.
So it tends to
rise and cooler more dense
air sinks. Before home refrigerators were
redesigned with fan cooled evaporators, boxes were equipped with
wire shelving allowing heated air to move naturally and slowly
tumbling in the box. With an evaporator at the very top of the
box, air below it tends not to stratify in layers. Warm air on
top and when cooled it drops.

Cooling is
the process of removing heat so heat removal inside an area
depends on a heat conducting medium (air) being able to surround
warmer items as much as possible and then return to the
evaporator where the heat is absorbed.

My
recommendation for a spillover refrigerator is this. Most boat
spillover boxes are side by side requiring pressurized air
movement to maintain individual box temperature control. One
thermostat controls freezer temperature by cycling compressor on
and off. A second thermostat controls a very small refrigerator
fan located in middle of divider. Return air to freezer is
provided by a hole at top of the divider. Install rails across
the bottom of the box and up both sides to insure that the lower
product stays frozen.

The
compressor must have capacity to handle planned worst case
cruising climate. The Evaporator should be installed in the
freezer covering as much wall space as possible and have equal
maximum capacity of the compressor.

The following are
Q&A’s that I have received on the above subject.

My refrigerator cabinet is
divided in half. Half for the freezer side and
half for the frig side. I am looking for a
thermostat control that will turn on the small
computer fan that pulls air in from the freezer
side to cool the frig side as it is needed. Do
you know where I can find one? The one I had was
a simple little mechanical deal that fit right
in the frig?

ANSWER: I don’t know of an
inexpensive fan control thermostat. The one I
sold is no longer available. Adler Barbour does
sell one but he problem is that the desirable
temperature range for these thermostats is 25 to
40˚ F. I have used a temperature controller for
this fan although it’s a little pricey at $60.
With a temp range from -25 to +40˚ it gives good
control and has a differential adjustment. It
can be mounted outside the box as it has a 60
inch remote bulb. These controllers are
available from several manufactures Ranco's P/N
is 010 1408 or equivalent.

Question:
Spillover performance: I
recently bought a sailboat with the intention of a world Pacific
(Bora-Bora) cruise three years from now. The boat came equipped
with a Danfoss BD35 with keel, water cooled. It has an
evaporator in an L shape of 30'' long that turns 90˚ and prolong
12'' more for a total length of 42''.The evaporator is 12''
high. The box is 9 cubic feet and includes a 2'' divider in the
middle 2'' in height smaller so the air could flow from one
compartment to the other. My question is: Does this set up act
as a freezer on one side and refrigerator on the other side or
is it only a large reefer? Should I modify it to have 1/3
freezer and the rest fridge by moving the separator towards the
evaporator? How close should the food be from the evaporator to
have a good heat transfer and stay frozen. Would it be a good
idea? Is it better to change the evaporator for a square one
instead of an L shape one? I have a 1200Amps battery bank, a
wind generator, a 110Amps alternator and am thinking about solar
panels.

Question: The box is urethane sprayed 5'' insulated factory
made. I intend to add a 1'' polyurethane panel (instead of
Styrofoam) wrapped in plastic and a 1'' bubble heat shield. How
does it sound?

ANSWER: Your BD35 compressor and L shaped evaporator with keel
cooler will do a reasonable job in seawater temperatures of 65
to 75˚F. A nine cu ft combination spillover box is too large for
the small BD35 compressor when cruising in tropical waters.
Spillover icebox conversions generally provide only short term
frozen food storage. The closer the frozen product is to the
evaporator the longer it will maintain its quality.

Adding insulation to the outside of the box will not improve
energy performance but adding extruded polystyrene (Moisture
Resistant) insulation to the box’s interior will, but it also
makes box smaller.

If I were you I would use the present box as a
refrigerator cooler and buy a stand alone
portable freezer like the ENGEL 45

Fused red power wire to
single pull single through a simple Off On switch.

Red wire from other side of switch to
thermostat.

Red wire from other side of thermostat to
red wire of fan.

Black wire of fan to a ground.

An area control thermostat is used instead of a refrigerator
evaporator thermostat in order to control refrigerator areas air
temperature in a suitable range 33 to 45˚F.

Best installation of a spillover fan is to
recess it inside one inch thick or thicker divider, mounted in a
one inch hole or mounted on the refrigerator side of the hole.
The Fan is located midway up divider and removes air from the
freezer pressurizing the refrigerator at less than 10 CFM.
Return air to the freezer is by a one square inch opening at the
top of the divider.

We are
looking at replacing the current system with a new AB Cold
Machine CU 100 and the 100 series evaporator plate rated for 15
cu ft. The boxes are SS. The freezer section is 3.3 cu ft, the
divider is 2" thick with holes at the top and bottom for
spillover. There is no fan currently installed. Fridge is 6.3 cu
ft. Insulation is 3~4 inches. The questions
are?
Can the system described above work as a spill over system?
Should the bottom hole be plugged and a duct be fabricated so
the fan pulls air from the center of the freezer to pressurize
the fridge side? Would it be better to use two smaller systems
and run them independently? Thanks!

ANSWER: Without knowing your planned cruising area I can not
verify if capacity of BD50 or an evaporator could handle a 3.3
cu ft freezer and a 6.3 cu ft refrigerator. The BD50 compressor
powered, condensing unit will be large enough for a 9.6
combination box when cruising the West coast of US or cruising
in north on the East coast. You need to watch the slide show on
my web site for equipment selection and a boat’s DC power grid
requirements. Above Latitude 36 N the daily amp-hrs consumed
would be maybe 70 daily. Cruising in the tropics daily amp-hrs
may reach 150.

Adler Barbour has changed hands five times
and now is lumped into Demitic’s inventory so I would need
evaporator description as Series 100 does not identify your
planned unit. For a freezer to function properly the evaporator
needs to be in the freezer surrounding the frozen product as
much as possible.

If the spillover divider plan is to be without a
fan, all holes presently there should be plugged
and later opened only enough to allow natural
air movement to achieve the temperature
separation you desire. My recommendation would
be to plug all holes in the divider except for a
one inch hole at the top of the divider. Then
install a 1/10 amp one inch square fan mid way
up from box bottom in divider. The fan should be
controlled by a separate special zone thermostat
(cooler type thermostat) sensing refrigerator
zone temperature.

Conventional home chest freezers use wire baskets to allow
natural air circulation throughout a box. Home refrigerators are
designed to assist in air tumbling circulation by having some
type of open shelving when the evaporator is located at the top
of the box. The evaporator absorbs heat from the air then cool
air descends absorbing more heat and rises back to the
evaporator.

A
circulating fan in a refrigerator or freezer will not produce
good results in a box without open shelving unless a series of
standoff rails are placed on the walls and floor to provide a
space for air circulation.

Top opening refrigerators and freezers on boats have poor air
flow and therefore the temperatures will vary from side to side
and top to bottom. Without air movement in a refrigerator or
freezer, temperatures tend to stratify in layers. Most
commercial and home refrigerators are constructed to allow the
natural movement of warm air rising and cold air descending
across the evaporator to tumble the air. The addition of a small
fan can help most refrigerated boxes. I recommend a one inch
square muffin fan that runs at all times when the refrigeration
is in use. I ran over two hundred tests to prove what works and
what does not. Many are in my 12/24 volt manual.

TUMBLING AIR FAN TEST:

The thermostat was locked and outside air
temperature maintained between 79 to 82˚F. for these 24 hour
tests. In test 119 the food product blocks the transfer of heat.
In test 120 the small airflow from a one-inch muffin fan
tumbling box air, lowered temperature eight degrees at the far
end of the box. This fan also increased the efficiency of the
evaporator and increased Btu output from the compressor.

Question: What about flashlight battery powered fan sold at West
Marine?

ANSWER: These battery fans do work and I have tested the
Fridge-Mat unit. It does run 30 days on one D cell battery.
These units were designed for the open shelving RV refrigerators
to assist the natural tumbling of the air in a box. I have no
idea how many months they will last as the motor looks like it
is out of a toy.

Boater REPLY: I had one for four years and
it worked all season(six months, only on weekends) on two D cell
batteries. I would still be using it but I dropped it and broke
it. I thought it made a big difference, enough so that I bought
another one (wal-mart less then $20) they help to avoid "warm"
spots in the cooler and help to cool everything evenly.

Performance and energy efficiency of any refrigeration unit
depends on the condenser’s Cooling Medium temperature.
Refrigerators are generally designed for optimum standard day
air temperature of 68 to 70˚F. Most small 12 volt boat
refrigeration units have long capillary tube, refrigerant
expansion devices that control refrigerant at a specific volume
of refrigerant flow. If the condenser’s cooling medium varies
above or below the manufacturer’s design temperature, a system’s
optimum performance will change. The reason performance changes
when the cooling medium temperature changes is that the
refrigerant’s high pressure increases and as temperature
increases it draws more current.

Home condenser cooling medium temperature do not change much
inside a home where creature comfort is maintained but when
installed in a boat ambient air temperatures do change.

The key to gaining the best
performance from small 12/24 volt refrigerators or icebox
conversion units is how correctly it is installed in your boat.
Using cabin air directly into intake side of condenser cooling
coil and using a fan to dispose of process heated air to an open
area so that it can not re-circulate again is what I mean by
correct installation. Some manufacturers elect not to use
positive displacement fan shrouds to insure all fan air capacity
flows through the condenser coil. These units should be avoided
if they are to be installed in a closed space. If you want peak
performance on an already installed unit, look at ways to better
direct air over the condenser coil. Standard designs for
condenser fan capacity on condensing units powered by Danfoss BD
compressors are to use four inch muffin fans with a cfm capacity
of around 60 cfm.

Twelve condenser fans are also available in
80, 100, and 130 cfm. The problems with replacing a small
capacity fan with a larger capacity one is that they are noisier
and higher cfm fans are 5/8 inch thicker than the original. The
larger 100 and 130 cfm fans can be connected to Danfoss BD2.5
and BD 3 modules direct because they draw less than one amp. If
a fan draws more than ½ amp it cannot be powered from the BD35
or BD50 compressor modules direct and a relay is required. For
tropical climates, my designed units all had 80 cfm fans. The
best thing about these little air cooled units is high
refrigerant pressure performance can be maintained in cool
climates by blocking a portion of condenser coil. Danfoss BD35
and BD50 compressor module condenser fans are always 12 volt
even when module and compressor are running on 24 volts.

Seawater Temperature Affect On Boat Refrigeration

QUESTION.
In your 12/24 volt manual section on selecting a refrigeration
unit you separate the units by what works in cold climates but
will not work in warm climates. On the Great Lakes
we have 90° days the same as they do in the tropics what’s the
difference?

ANSWER: The seawater’s temperature surrounding
the boat’s hull has a major effect on the ambient air
temperature inside the boat and plays an important role in the
performance of a refrigeration system. Cruising area seawater
temperatures are not listed as part of a refrigeration sales
brochure but should be. Water temperature also must be
considered if the refrigeration equipment selected is to be
water cooled. Failure to consider the effects of different
seawater temperatures when selecting a boat refrigeration system
is why many refrigerators perform poorly.

Good boating weather
is when the temperatures are in the 70° to 90° F. range. In this
country when there are good boating temperatures the water
temperatures can vary in the north from 50° to 98° F. in south
Florida the Bahamas and the Caribbean. When you think of California
having good boating weather we forget the Pacific ocean
is cold. Example, weather Station 46025 - Santa MonicaBasin in
August reported a seawater temp of 69° while Station FWYF1 -
Fowey Rocks, FL the same day reported 86.7° F.

Ambient air and
seawater temperature along with the box’s insulation and
intended use, will determine the size and type refrigeration
system for a particular boat. There are formulas for calculating
the Btus of heat effect on large walk-in refrigerators that some
think can be scaled down and used to project a small boat
refrigerators total heat load. I believe the estimated heat load
should be based on worst case conditions such as: Thermostat set
to maintain 33° in the coldest part of the refrigerator box,
normal daily product flow in and out of the box, number of
people on board, ambient temperature of 90° F. and seawater
temperature of 86° F. If the box has a front opening door add
infiltration heat loss. Using the method in my book for a six
cu. ft. refrigerator box in worst case conditions, with three
inches of good foam insulation, four people on board and a 14
inch front opening door, the heat load would equal 6440 Btu per
day. If the boat were in Santa Monica CA. instead of in the
tropics where the seawater was 17 ° cooler there would be a 20%
to 30% reduction in the daily heat load projection. In this same
comparison if the condenser were water cooled a 34% reduction in
required daily Btus are possible. The problem with seawater
cooled condensing units is they begin to loss efficiency when
the water temperature drops. If the same water cooled unit that
was designed for the tropical conditions above were operated the
same day on a boat at Station 46026 - SAN FRANCISCO
with a water temp of 54.5° its performance will be less than
good. When selecting a refrigeration unit you want to error on
the cool climate side not the hot climate side.

On pleasure boats when
the refrigeration compressors are larger than 1/6 Hour power the
process heat is almost always removed by seawater. Maintaining a
reasonable temperature range of the condenser cooling medium,
air or water is important, too low or too high a temperature
will affect the system’s performance. Large commercial water
cooled refrigeration units have water flow regulators to
maintain the high side pressure in a system, but they are not
available on the small systems. Two of the pioneers in pleasure
boat water cooled engine driven refrigeration, Crosby and
Grunert, used manual seawater bypass valves to keep the high
pressure refrigerant in the proper range. With an adjustable
water bypass the same system can operate efficiently in the
Pacific or the Caribbean.
It seams like refrigeration systems manufacturers located in
cooler water climates tend to error more when it comes to
adequate seawater cooling for use in the tropics. The small
refrigeration compressors with capillary tube expansion devices
are very sensitive to temperature variations in the cooling
medium, therefore, water cooling is a poor choice unless
operated in 55° to 75° F. waters. Small air cooled condensing
units are much more suited to varying air temperatures. Adler
Barbour and Technautics are two of the companies that design
with adequate air cooling for the tropics and if the same units
are operated in a very cold climate the airflow across the
condenser can be restricted or a portion of the air recycled.

QUESTION

:
Last
fall I added an additional vent and muffin fan to help cool the
enclosure of my 8 cu ft. marine fridge. I have the fridge out
and am trying to decide if I need to change where the fan is,
direction etc. The compressor and condenser are located at the
lower rear of the unit in a cutout across the back and the fan
on the condenser sucks air from left to right - looking at unit
from the front. Air goes thru the condenser then over the
compressor and then the electronic unit for the compressor.
As luck
would have it all vents are on the right side of the enclosure
toward therear; two near bottom ( lowest one has my added fan )
and one up high. With the unit
installed, there is about 4 inches of air space on sides and
back. I think some
type of cross ventilation across the lower back of the unit
would be best but that is not possible on my boat. My
question concerns the aux fan. Right now it blows in on the
lower vent and I am wondering if that fights the airflow going
in the other direction from the condenser fan. Should I reverse
it to pull air from the lower vent? Or should I be pulling air
with the fan on the upper vent. Not really sure what is best?

ANSWER:
Because I can not look at the physical configuration of your
refrigerator’s heat removal system, I can not provide detailed
help in improving performance. Refrigerators sold for RV
applications and sometimes used in boats will have problems in
warm weather disposing of their process heat. The only way to
cool an area is to remove the heat in that area and send it
somewhere else. The compressor pumps refrigerant through the
system which picks up heat that must be disposed of by a
condenser coil.

Many refrigerators have large vertical
static air condenser coils mounted on rear of the cabinet to
dissipate heat to outside air by natural air movement. Natural
movement of air on this type unit is IN at the bottom and
exiting warm air OUT at the top. If a refrigerator is to be
built into a cabinet the exiting air chimney size is listed in
the installation instructions, Example, Norcold lists 100 sq.
inches.

On refrigerators where the condenser is cooled by forced air
from a fan, air must be guided from an area containing air with
low ambient air temperature into the shroud of the fan. The
shroud insures that all of the fan’s air passes through the
condenser coil by pressurizing the area between the fan and
coil. After heated air leaves the condenser it is still under a
small amount of pressure and must be guided by baffles to an
exit point that prevents it from re-circulating back to the
condenser fan a second time.

Additional heat removal fans are sometimes
required to assist in process heat removal to
another area but they are of no use if they only
circulate air in the same warm compartment.

QUESTION:
increasing condenser fan
capacity

Thanks
for all the help you gave via e-mail, both BD 35 units are
running well, fully frosted evap plates, with nominal temp lines
to and fro the compressor. I have received
a pair of fans with 108 CFM airflow to replace the supplied
units at 89CFM, but even though the new fans are spec 50ma,
neither will run more than a few seconds before shutting off.
Supplied fans are spec 37ma. Perhaps start up current is
exceeding allowable current.
Two flash code is displayed on one unit, but the other unit
seems to have a faulty LED which I'll have to test and replace.
Kind of odd, but both units are behaving identically.
The LED gets positive from the power SW, so the Neg leg must be
controlling the flash patterns when present. A relay is no
problem, but I'm thinking that I'll direct wire the Condenser
fan to the power SW, and add fans on the Current limited circuit
aimed at the control unit fins. What do you
think? This would avoid a relay and provide extra cooling. Also, how
should an LED be wired to cycle with the Compressor? Via the Fan
limited current circuit? Both Compressors mask each other noise
wise, so led's to indicate cycling would be good. What resistor
value would be used on these LED's?
Thanks again,
Chris

ANSWER:
There are two
terminals on Danfoss’s variable speed control modules designed
to operate cooling fans that draw less than ½ amp, these
terminals are the small + and F. Presently on your BD35 modules
the red + wire from fan is connected to the modules small +
terminal not large + terminal and black fan wire is connected to
F ground terminal. This small + and F electrical circuit is
energized when compressor is running. Should fan begin to show
signs of failure by drawing more than ½ amp electronic control
module will stop compressor. When brushless (muffin) fan’s load
is less than 80 CFM normally it will be less than ½ amp. If your
plan is to add additional load to this fan circuit then another
source of 12 volt power can be provided by a relay.

Adler Barbour’s CU models already have a
relay for add-on 12 volt accessories. Other manufacturers use an
inexpensive Auto relay pictured on page 43 of my 12/24 volt
refrigeration manual. Last time I was at Pep Boys this relay was
under $3. Electrical drawing above relay on page 43 is for fixed
speed compressor modules. All of these inexpensive automobile
relays have two coil terminals 85 and 86 and two or three load
transfer spade terminals Fused power source is connected to
terminal 30 and Fan load (red wire) to terminal 87. If relay has
a fifth terminal 87A it is normally closed and not used. All
Danfoss BD compressor systems use this type relay on water
pumping condenser systems.

Refrigerator run LED you want would also be
connected to same terminals as fan. As far as 12 volt LED
resistor I would recommend one already designed with resister
built in like Radio Shack P/N 276-270A, but Green colored. I
have used a 370 ohm resistor on plain LEDs before but wattages
are not the same on all LEDs. If you use a plain LED you need to
get its polarity correct. If LED is for the troubleshooting
circuit its current must bi 20ma or less.

Condenser Fan AC/DC 101N500
Module

QUESTION:
The compressor and fan would run fine on 120VAC but on 12VDC the
compressor would bump during which time it almost sounded like
an old style analog modem with sound coming from the control
board. The fan would turn on and then both would shut off. The
LED I had installed would present a 2 flash code, fan over
current. We rechecked the 12VDC wiring and all was in good shape
(less then 10 ft run of #6AWG to fully charged 440ah house bank
battery's) I removed the control module and cleaned all the
terminals with no luck. I then replaced the fan with a lower amp
draw fan and it seems to have fixed the issue. Do you know if
the fan is a common problem with these units? This is an Nova
Kool RFU8220 model.
Sean

ANSWER:Module, small Plus + and F terminals, for
fans are limited to 1/2 amp and 12 volts. When an electrical
load on these terminals exceeds 1/2 amp, the module will assume
the compressor may be over heated and will stop the compressor.
If the fan motor bearings are dry and about to fail or any one
of its many internal transistors is week, amperage will exceed
1/2 amp and willstop the compressor. Life expectancy of Muffin
brushless fans with ball-bearings instead of bushings in a live
aboard boat last from five to seven years.

Replacement 12
volt 4.68 inch muffin fans are available in several CFM ratings
from 35 to 100 CFM. And draw from .35 to .50 amps. If cruising
in the tropics, the 80 to 100 CFM fans are the most efficient
but as the CFM is increased the noise level is also increased.
These are very common fans and can be found at most electronic
stores.
Www.mouser.com
phone 800 346-6873 has the ball bearing replacement fan for $13.
WWW.Rparts.com also sells replacement fans rated at 60 cfm and
95 cfm their cost is $40.

A condenser fan is replaced by removing the
four sheet metal screws on the fan corners. Then disconnect the
small red and black wires from the unit’s electronic control
panel or terminal strip on some models. Be sure to remember
which terminals are red and black. If you purchase the higher
output fan it may be one inch thicker so longer number 8 screws
will be needed for the replacement. It is also possible on some
manufacturer’s fans that the mounting holes may need to be
drilled to accommodate the number 8 screws. The most difficult
condenser fan to remove is on Adler Barbour CU 100 and CU200
condensing units as the fan is located inside the shroud. On CU
units remove the pop rivets holding the shroud to coil. Next
disconnect fan wires and remove screws inside shroud to get fan
out. Because the space on Adler Barbour’s CU models is so tight
only the one inch thick fans with lower cfm will fit as a
replacement.

QUESTION What about a fan to improve evaporator
capacity when evaporator is too small for compressor’s Btu
Output?

ANSWER: It does not make any difference whether
the refrigerant flow is provided by 12 volt or 110 volt energy
if the output energy is greater than the capacity of the
evaporator or holding plate. Repeated compressor cycling before
desired box temperature is achieved can indicate surface area
heat conduction of evaporator or plate is insufficient and
adding a fan that causes convection heat transfer can improve
overall system efficiency.

Module overheating may be the
primary reason for so many electronic control module failures.
Through the years Danfoss has designed static air heat sinks on
modules to conduct and radiate heat away from transistors and
other components inside the module. Module heat increases as
compressor load (amperage) increases. Danfoss’s installation
application data sheets have always assumed system designers and
installers would insure compressor design power amperage limits
were not exceeded. What you will find in the marine industry is
the elimination of module and compressor cooling air along with
higher than design compressor heat loads. Only Danfoss’s AEO
modules have built in module cooling fans. Danfoss’s variable
speed specifications for BD50 require an additional fan for
cooling the control module if the compressor is to be operated
at maximum capacity (3500 rpm). This fan is in addition to the
condenser fan air. All of the following conditions can cause
module overheat failures; High condenser cooling temperatures;
Repeated attempts to start due to an overloaded compressor;
First box temperature pull down in a hot climate; System ambient
temperatures above 105˚F, and too large or poorly designed
holding plate evaporator coils. Failure to maintain good cool
flow of condenser air, a normal maintenance item, should not be
overlooked as cause of module failure.

All electric hermetically
sealed compressors rely on cool return
refrigerant gas for cooling of the compressor.
When the compressor is exposed to maximum heat
loading, the condensing unit’s fan airflow
provides additional cooling for the compressor.
On water cooled refrigeration, the manufacturers
have added water cooling jackets clamped to the
compressor or fined heat sinks in an attempt to
cool compressors. On unfriendly water cooled
systems like the ones using 12/24 volt Danfoss
BD compressors I have always recommended adding
a compressor cooling fan. If BD compressor is
allowed to run hot so will its control module
run hot causing it to fail.